Low power features of processor based platforms are useful for mobile computing, to increase battery life of devices such as notebook computers, handheld computers, “smart” phones, among many others. Similarly thermal requirements in processor based platforms such as densely packed servers may make it important to control power use in such environments. Power efficiency is important for processor based platforms in general, and therefore features to support lower power use may be incorporated into many different types of platforms. Such features may include, for example, gating or turning off portions of logic, lowering operating frequency, dimming displays, and many others. These features may be incorporated into chipset and processor cores.
Current implementations rely upon stringent control over applications and services that are run on a platform, such as in current mobile handset designs for low-power use. This may not be practical for an open platform that needs to support very long standby times.
The Advanced Configuration and Power Interface (ACPI) specification defines an Operating System (OS) directed power management interface that includes system and device power states, as is well known. The specification is available at www.acpi.info on the World Wide Web.
In typical processor-based platforms, there at least two types of interrupts that may cause a processor to exit an idle or low-power state and become active. The first type of interrupt is caused by various types of timers that may be used by an operating system, as is known in the art. Other types of interrupts are event driven and caused by events, such as an external input event, failure conditions, among many others.
In some processor based platforms the duty cycle of a processor may be varied. For each time slice, the processor may be operated in a fully active mode only for a fraction of the time in the time slice, and be idled for the remainder of the time in the time slice. This fraction is termed a duty cycle.